a. Field of the Invention
The present invention concerns a method for inserting data onto one or more vertical blanking interval lines (or VBI lines) of a television video signal, and in particular, for inserting data (such as non-video data) onto one or more VBI lines of a television video signal conforming to the NTSC (National Television Standards Committee) format. The present invention also concerns a device for implementing this method.
b. Related Art
Vertical blanking intervals of video signals conforming to the NTSC format have been used for carrying inserted data, such as closed captioning data for example. Although the NTSC format is well known in the art, a brief description of its salient aspects is described with reference to FIGS. 1, 2, 5a and 5b. A color video signal must convey luminance, hue, and saturation information. Luminance information is perceived as brightness, hue is perceived as color and saturation is perceived as color purity. The NTSC standard facilitates recording, transmitting, and playing back this information.
The NTSC standard provides 525 horizontal lines of video. The television receiver "scans" the horizontal lines onto its screen, from left to right. After the scanning of each horizontal line, the scanner requires a small time period to reposition itself at the left of the next horizontal line. This is known as horizontal retrace. A sequence of horizontal lines is scanned from the top of the screen to the bottom of the screen. Each image frame consists of two interleaved fields. As shown in FIG. 2, the two interleaved fields consist of a field of odd horizontal lines 201, and a field of even horizontal lines 202. Each of the fields consists of 262 or 263 horizontal lines. At the end of a field, the scanner requires a period of time to reposition itself to the left of the first horizontal line of the next field. This is known as vertical retrace.
FIG. 1 depicts a waveform for one field or one half of one frame. The waveform includes four components; namely, the picture waveform, horizontal and vertical blanking pulses, synchronizing pulses, and equalizing pulses. For about the first 240 horizontal lines of the field, each line of the waveform includes a horizontal synchronization pulse superimposed on a horizontal blanking pulse, which is followed by a picture component. The horizontal blanking pulse consists of about 14% to 18% of each line and causes a dark output during the horizontal retrace time. The horizontal synchronizing pulse is superimposed on the blanking pulse and is used to maintain the timing of the picture tube scanning. The horizontal synchronizing pulse is defined by the leading edge of the pulse. The picture waveform includes signal variations which correspond to variations in the brightness (or luminance) of the picture. The luminance signal (E.sub.y ') is based on the relative sensitivity of the human eye to primary colors (i.e., red, green, and blue). The picture waveform defines the so-called "active period" of each scanning line. If the amplitude of the signal is 100% for synchronizing pulses, the amplitude of the picture signal will be between 7.5% (representing white) and 70.0% (representing black) of the amplitude of the synchronizing pulses.
The remaining of the 263 horizontal lines of the field (i.e., horizontal lines 241-263) occur during the vertical blanking interval (or vertical blanking period) which constitutes about 7.5% of the vertical scanning interval. The vertical retrace of the scanner occurs during the vertical blanking interval. As shown in FIG. 1, the first 9 or 10 lines of the vertical blanking period include equalizing pulses and vertical synchronization pulses. The equalizing pulses prevent the pairing of interlaced lines on the picture tube. Specifically, for odd-numbered fields, the leading edges of the vertical synchronization pulses coincide with the horizontal synchronization pulses, while for even-numbered fields, the leading edges of the vertical synchronization pulses do not coincide with the horizontal synchronization pulses.
FIG. 5a illustrates two lines of chrominance information superimposed on two lines of the luminance signal (see, e.g., period V--V of FIG. 1). The hue is determined by the phase of the subcarrier, and the saturation is determined by the amplitude of the subcarrier. As shown in FIG. 5a, and in greater detail in FIG. 5b, a "color burst" consisting of a train of sine waves is placed on the "back porch" of the horizontal blanking pulse at the start of a new line. The phase of the subcarrier, and thus the hue, is determined with respect to the sine waves forming the "color burst."
Lastly, NTSC standard specifies a transmission rate of 29.97 frames per second, an aspect ratio (i.e., the ratio of image width to image height) of 4/3 and a horizontal resolution of 340. Since there are 525 lines per frame, 15,734 lines are must be scanned per second. The subcarrier frequency of the chrominance signal is 3.579545 MHz.
FIG. 3 illustrates the format of a closed caption waveform 300. The temporal length of the closed caption waveform 300 is approximately 2 ms. As shown in FIG. 3, the closed caption waveform 300 includes seven (7) cycles of a sine wave 310, a low bit, a low bit, and a high bit (or a "0-0-1" sequence) 320, and a two (2) byte payload section 330. The two (2) byte payload section 330 includes the closed caption data. In the NTSC format, close caption waveform 300 is inserted on the 21.sup.st line of one or more vertical blanking intervals of the first field of one or more frames.
A suitably equipped television receiver (hereinafter referred to as a "closed caption compatible television receiver") includes a means for stripping the closed caption waveform 300 from a received NTSC video signal, a means for decoding information contained in the closed caption waveform 300, and a means for providing a display of the decoded closed caption information.
The seven (7) cycles of a sine wave 310 allow a closed caption compatible television receiver to lock onto the phase of the closed caption waveform 300. By locking onto the phase of the closed caption waveform 300, the television receiver can read each of the sixteen (16) bits of data in the two (2) byte payload section 330 in the middle of the bit, away from any rising or falling edges. The 0-0-1 sequence 320 indicates that the two (2) byte payload section 330 will follow. The two (2) byte payload section includes textual information to be displayed on a portion of the video output of the television receiver. Since each closed caption waveform 300 includes only two (2) bytes of data, a series of closed caption waveforms 300 must be inserted on the first field of each of a sequence of video frames. Typically, this textual information permits deaf and hearing impaired television viewers to follow the dialog of a television program.
LSI Logic Corp. provides an MPEG-2 Audio/Video Decoder, model no. 64002, which includes registers for inserting data onto a vertical blanking interval. Data stored in these registers may be used for closed caption data and for VITS (Vertical Integral Test Signal). The registers include two (2)-eight (8) bit registers for storing the address of luma (luminance) data to be output during the vertical blanking interval and two (2)-eight (8) bit registers for storing the address of chroma (chrominance) data to be output during the vertical blanking interval. However, the origin of the address to be stored in the registers is not identified. Moreover, the registers are described as storing addresses, not data.
In view of the limited types of data inserted on the vertical blanking interval of a video signal in the known systems, inserting other data, such as non-video data, and in particular, textual data, onto the vertical blanking intervals of the NTSC formatted video signal may be desired. For example, advertisers (sponsors) may want to verify that their advertisement (commercial) was successfully transmitted, in its entirety, on a particular channel at a particular time.
Historically, video programming has been provided by local television stations which transmit analog signals to the homes of viewers within the transmission region of the local television stations. Such video programming has been either publicly funded (e.g., PBS) or privately funded by sponsors (e.g., firms, public interest groups, politicians) wishing to convey an advertisement to potential viewers of the video programming.
Over the past decade or two, "off-the-air" analog communication systems, such as cable television (CTV) systems for example, have become common. In cable television systems, a number of channels are frequency multiplexed and transmitted onto a coaxial cable distribution network. Due to the limited bandwidth of the coaxial cable, only about 50 to 70 analog video channels can be simultaneously carried over an appreciable distance without undue signal attenuation. A set-top box at a subscriber's home decodes a selected channel from among the channels frequency multiplexed on the coaxial cable entering the set-top box. The programming on these channels may be publicly funded and/or privately funded, and in each case, the funding may be supplemented by money paid by subscribers of the cable television service.
In the past few years, digital satellite systems have entered the market for providing video programming to individual consumers. Although digital transmission and compression permit a large number of channels to be transmitted a relatively great distance without signal degradation, each subscriber needs specialized and relatively expensive satellite receivers, digital decoders and decompressors. As with cable television (CTV) systems, the programming on these channels may be publicly funded and/or privately funded, and in each case, the funding may be supplemented by money paid by the subscribers of the satellite video programming service.
In each of the above systems, advertisers (sponsors) may, and often do, substantially subsidize the costs of providing video programming. In return, the advertisers are able to convey their message to a relatively large potential audience. The advertisements (commercials) may be run nationally or at the local level. Although nationally run advertisements have the potential of reaching the largest audience, they are relatively expensive and inherently not targeted to a particular geographic region. On the other hand, locally inserted advertisements are relatively inexpensive and have the potential of reaching a more specifically defined geographic audience.
The following provides an example of the insertion of a local advertisement on a network program (national) video feed received at a local station. Conventional subscriber systems, such as cable television (CTV) systems, are typically arranged to provide viewer programs according to a predetermined time schedule. The programs available to the subscribers of a particular system are usually provided by a national network source and transmitted, via a satellite link for example, to the head-end of a local cable television distribution system. The national network programmers provide certain intervals (i.e., designated breaks) during each program. The local cable provider can provide content (e.g., local advertisement(s)) during these designated breaks. For example, approximately four minutes are commonly set aside in each half-hour of national network programming to permit local insertion of commercial advertisements that may be particularly targeted and relevant to the local subscribers of the cable television (CTV) system.
The time of each break is generally indicated by a "cuetone" signal which is delivered as a part of the national network feed signal. The types of cuetone signals that may be transmitted in the national network program feed include: i) a pre-roll period signal which allows a video tape player, loaded with a video tape having a local advertisement, to attain operating speed and to advance the video tape to the start of the advertisement; (ii) a transfer-to-ad signal which indicates the start of the advertisement transmission interval; and (iii) a return signal which indicates a return to the national network program source transmission. The cuetones are formatted as standard dual-tone multi-frequency (DTMF) signals. A local program programmer may substitute local advertisements in the place of national advertisements during the designated breaks indicated by the cuetone signals.
Two possible operational sequences of advertisement insertion are briefly discussed below. In a first operation sequence, a series of cuetone signals detected by a cuetone detector serve as inputs to a controller. In response to a pre-roll cuetone signal, the controller activates a local video tape player, which has mounted thereon, a video tape containing the desired advertisements. When the controller receives the transfer-to-ad cuetone signal, it commands switching equipment to switch the subscriber system from the incoming national network program video and audio signals to the output of the local video tape player for the duration of the advertisement. Finally, when the controller receives the return cue tone signal, it commands the switching equipment to return the subscriber system to the incoming national network feed.
In a second operational sequence of the advertisement insertion, only the pre-roll cuetone signal is required. In this instance, the local cable programmer knows that, for the given cable channel, the pre-roll time is a fixed interval and that each break is of a fixed duration. When the controller receives the pre-roll cuetone signal, immediately following the fixed interval, the switching equipment switches to the local advertisement. At the end of the fixed duration break, the switching equipment switches the subscriber system back to the national network feed. Thus, in this example, transfer-to-ad and return cuetone signals are not required.
In any of the above mentioned systems, an advertiser (sponsor) will want to verify that its advertisement was properly stored, retrieved, switched to, and transmitted on the appropriate channel at the appropriate time. Moreover, the advertiser will want to ensure that the commercial ran in its entirety. Although such verification is important for advertisements inserted nationally as well as locally, the verification of locally inserted advertisements can be more complex since the number of local markets can be large.
As discussed above, cable television (CTV) systems, for example, permit advertisements to be inserted locally. Again, typically, cuetones in a national network program feed are used to signal when an advertisement is to be inserted. Specifically, based on cuetones, a switch having inputs provided with a national network program signal and a local advertisement signal, will output one of these signals for transmission onto a channel of the coaxial cable distribution network.
The prior art does not provide a method or device for verifying that a commercial was properly transmitted, in its entirety, on an appropriate channel of a coaxial cable distribution network at an appropriate time. Therefore, a need exists for such a verification method or device.